Synchronously operated regulator



A. M. COHEN 2,654,063

SYNCHRONOUSLY OPERATED REGULATOR Sept. 29, 1953 Filed June 5, 1948 Patented Sept. 29, 1953 UNI-TED STATES. PATENT OFF ICE.

2,654,063 SYNCHRONOUSLY OPERATED REGULATOR- Arthur-M. Cohen, New Yul-arty. Application June 5,1948;Serial'No: sem

19 claims, (01. 32116) The present" invention relates to the: connectionandioperation :ora regulator-adaptedjto'com trolintermittently supplied electrical energy and tea method of' capacity of such a-=regulator;

The-typeof regulator to whichthepresent irrvention is" particularly adapted for use and with respect to which the: invention is herein i1lus-- trated-is the so called finger type, which is. constituted of a" plurality of regulatory circuit elements such as: resistances and a plurality of contact pairs, one member. of each pair being carried by-a=movable-finger. I he fingers-may be moved-in any desired manner-so as to successively open and-close the contact pairs and thereby-suc--- cessively connect and disconnect the regulatory circuit-elements in the circuit, therebyvarying theenergy loss in said elements-and hence inversely varying the energyavailable to the load. In-this manner, the load. voltage, for example, may-be rendered constantdespite limited variations inthe source voltage, the contacts being opened and: closed according to thevoltageat the-loadso thatasthat voltage tends to increase, more resistance is inserted into-the circuit, thus maintaining the.

voltagcat'the load substantially constant;

Oneoftheprimary li'mitingfactors in the use ofregulators of this type has been their current carrying capacity;- Most critical in this respect are the contact pairsthemsel-ves, since; those con.- tactpairsor at least one of them at. any given the full current supplied time; carry; substantially to the load; When any givencontact pair isse'par'at'ed. by appropriate movement of' the finger which carries one ofthe contacts, the currentis: interrupted and, if itsmagni'tude is sufiicient; an:

arc will ten'd to formbetween the separatin'gcontacts. Thisnot onlycauses exce'ssive heating of" the contacts Y themselves but also results the W911 kh'OWfi phenomena-- OI pitting and metal.

transfer; As the magnitude of the currentim creases; the importance of theseeffects also increases andiif the current exceeds acertain critical value,- the. arcing and attendant self-destruc-= tion of the contactswill soon render the regulator un'dependable if not absolutely unuseable.

'I'heabove disadvantages have in the past not proved'of'materialsignificarice because the regulators in use were sufliciently massive so that they were adeqii'atefor almost all applications; Moreover, byyr'easonof their massive construction, tii moving' parts thereof had such great inertia as'to be. relativeiyinsensitive to rapid fluctuations inioiirrent. Airecentd'eveio ment'inthisfieidhas been the fabrication of exceedingly" small and increasingthe: current carrying:

to devisea regulator systemwhich has a'greater.

current carrying' apacity than has been attainable heretofore; By-the present invention, the contacts themselves, which formerly were the determiningfactorinsofar ascurrent carrying capacityis concerned, no longer limit saidcapacity in any way;.

Another. objector the present invention is to devise a method of employing :finger type voltage regulators, andin particular such regulatorsof small'size, so as to render them capable of regulating; currents I of high. magnitude.

A morespecific objectof the present invention isto-soconnect a-fin'ger type regulator into a circuit in which current is onlyintermittently suppliedrto a-load-as to synchronize the opening of any given contact pair with the intermittent passage ofcu-rrent therethrough, to the end that the maximum amplitude ofcurrent and even the average amplitude thereof, no matter. how high,

has: no deleterious or destructive. effect upon th contacts.

The..above.generalized.-objects are achieved by opening a given" contact pair only during the period between the intermittent current supply ing periods.v By so doing, noarcing whatsoever will take place at the contacts, since no current is being carried by. them-(as they are opened. As a result, a given regulator may carry currents greatly. exceeding those capable of being carried by regulators connectedin the circuitin conventional'manner; Thetiming'and control of the opening of the contacts is' in turn. achieved by energizing "the" contact openingmechanism from the intermittently"supplied'current and by varyingthe phase of theenergizing current so as to compensate'forthe mechanical stiffness" or inertia of the=contact openingmechanism.

To the accomplishment of the above objects andsuch other obiectsas may "hereinafter appear;- the present invention relates to an improvement'in' the methods! connecting-a voltage reg ulator in a circuit in which electrical energy is intermittently supplied to a load and to an improvement in a regulation system as defined in the appended claims and as set forth in this specification, taken together with the accompanying drawings, in which:

Fig. 1 is a schematic circuit representation of one application of the present invention in which half wave rectified direct current is supplied to a load from an alternating current source;

Fig. 2 is a graphical representation of the current and voltages present in the circuit of Fig. 1;

Fig. 3 is a schematic circuit diagram illustrating another application of the present invention in which full wave rectified direct current is supplied to a load from an alternating current source but in which a blocking condenser is employed to periodically interrupt the full wave rectified direct current; and

Fig. 4 is a graphical representation of various of the currents and voltages active in the-circuitof Fig. 3.

My invention is here illustrated as applied to a finger type regulator having a plurality of resistors 2, l, 6 and 8 constituting regulatory circuit components (Four resistances are shown by way of example only. The number may be increased at will), a plurality of fixed contacts i6, l2, M and IS, a plurality of movable fingers I8, 29, 22 and 24 each adapted to make and break electrical connection with the fixed contacts l0, l2, l4 and 56 respectively and defining contact pairs therewith, an actuator 26 for moving said contacts so as to successively open and close the contact pairs, the actuator 26 being shown schematically by means of a broken line, and an actuator-moving electrically energized element such as the coil 28 for controlling the movement of the actuator 26 and hence the opening and closing of the contact pairs. This regulator is connected into a circuit comprising a current source generally designated S and the load L. The actuator-moving electrically energized coil 28 is connected in the circuit so as to be energized by the interrupted 'current'and a phase shifting circuit generally designated B is employed in conjunction with the coil 28 so as to controllably vary the phase of the current active therein in a manner to be described more fully hereinafter.

As illustrated in Fig. 1, the source S supplies.

an alternating voltage illustrated in Fig. 2 by means of the solid lines 30, 30 and thebroken line 32. The regulator'circuitcomponents, the resistors 2, l, 6 and B, are connected iri'se'ries between the source S and a half wave rectifier 3 3, which may take the form of a selenium cell rectifier or any other half wave rectifier known to the art. A short-circuiting connector 38, in conjunction with the fingers I8, 26, 22 and 24 to which it is electrically connected, serves to shunt or short-circuit the resistors 2, 4, 6 and 8 out of the circuit. The coil 28, which constitutes the actuator-moving electrically energized element, is connected across the load on the opposite side of the rectifier 34 from the resistors 2, ii, 6 and 3 and may be provided with a series connected protective resistance 38. An adjustable condenser MI is connected in shunt across the coil 28, the condenser 4a constituting the phase shifting component or circuit B. A filter condenser 62 may be connected in shunt across the load in order to smooth the current impulses supplied by the sources through the rectiilfir '4 34 so that the load L may ultimately be provided with a more constant current supply.

Since the rectifier 34 is of the half wave type, it will be apparent that, although the voltage from the source S will continuously pass through a complete sinusoid as illustrated by the broken and solid lines in Fig. 2, the current supplied by the source S, and hence the current passing through the regulator, will be periodically interrupted and will take the form illustrated by the solid lines 3d, 38 of Fig. 2. Hence, current will flow only during half of each cycle of the alternating voltage.

Regulators of the finger type normally function in the following manner. When the voltage at the source S is of the proper value, all of the fingers i8, 20, 22 and 2d will be in electrical connection with their respective fixed contacts l0, i2, is and i6, In this condition, all of the resistors 2, l, 5 and 3 are short-circuited and in efiect are not inthe circuit at all. If the source voltage should tend to rise, the voltage at the load will also tend to rise and since the coil 28 is connected across the load, an increased current will fiow through it. It will therefore move the actuator 25 and will, for the circuit shown in Fig. 1, break electrical connection between the finger l8 and the fixed contact H3. When this has been accomplished, the resister 2 will be in series in the circuit and hence a voltage loss will take place in it, thus reducing the voltage at the load. If the source voltage continues to rise, increased current in the coil 28 will cause the breaking of electrical connection between the finger 20 and the fixed contact [2 so that the resistors 2 and 4 will be in series in the circuit, thus further reducing the voltage-at the load and so on.

It will be noted that with the fingers in their position shown in Fig. 1, in which all of them are in electrical connection with their respective fixed contacts, substantially al1 of the current passes through the contact pair ll], l8. If

this pair be opened while current is flowing, substantially the entire current supply to the load must be broken between the contacts 10 and I8, and. similarly with each of the other contact pairs as they are successively opened.

The coil 28 which controls the motion of the fin ers I8, 20, 22 and 24 via the actuator 26 will,

in the circuit of Fig. 1, be energized by the pulsating or intermittent current which the rectifier a l permits to pass. It therefore will, if the voltage should increase, tend to move the actuator 26 in accordance with those surges of current. The actuator 26 and fingers I8, 20, 22 and 24 are naturally possessed of some inertia and consequently will not move instantaneously in response to the intermittent surges imparted to them by the coil 28 but, if the actuator 26 and the fingers i8, 20, 22 and 24 be of sulficiently small size, they nevertheless will tend to move in an intermittent manner. If then the phase of the current flowing through the coil 28 be properly related to the phase of the current passing from the source S through the contact pairs and be also properly related to the inertia of the actuator 26 and the fingers I8, 20, 22 and 2 so as to ensure that the initial separating movement of each of the contact pairs will take place, or at least commence, only during the period between pulses or surges of current, then opening of a given contact pair will not result acccoaa intarcing andhencefthe nicotine-contacts. and fingerswill begrcatlyincreased.

While it; may, accidentally happen;, in a: iven. installation; that-ither circuit constants; are suchthat: such. synchronous: opening, of; the contact. pairs iszaccomplished, hatz situation-is: e cc dr ingly rareand: completely-- unpredictable. Moreover; ,asthe circuit ages ones it .is exposed-tovary ing-temperatures on thelike, its circuit constants: Willprobably vary; sufliciently so thatsynchronous operationwill no longer: take place. I. therefore providethe; adjustable condenser 40: connected in. shunt acrossthe coil 2:8,.this condenser having. the. effect. of: shifting the phase: of the current; in. the? coil 28:. It. is; contemplated: that; after a: givenv installation has. been accomplished. the. condenser 40: will be manually adjusteduntil nospark-ing; is observed at. the; contact pairsas: the

sourcevoltagevaries, this: being indicative :of the; fact that; the-contact-pairs are opening whcnno; current is passing through them. Eornioreaccurate adjustment, a. test oscilloscope may be used... Qnce this,- adjustrnenthas been'made, the regulator. even one of exceedingly. smallsize, may. carry line currents of very great magnitude. since thecontactsare not affected thereby. Shouldthe synchronous-adjustment shift, either because of variations in temperature, deterioration of a circuit element or the like; the circuit maybe easily readjusted for synchronous regulation. merely by readjusting. the condenser 40..

The desired phase relationship may also. be achieved mechanically, by so varying the mechanical constants of the moving parts of the. regulator,v and in particular. their. weights, the. rate of response of the dash. pot, if one is employed,.and the-resistance to flexingof thefingers Hi, 2'], 22 and 2.4,es to give to the regulator anrin ertia of.- proper value. Additionalelements. may be addedto the mechanicalsystem for the same. purpose,

The circuit of Fig. 3 disclosesanother method. of utilizing thesame regulator, as illustrated'in- Fig. 1 but. in.a different circuit. In Big. 3, a seleniumcellrectifier bridg 44. is. employ-ed to: give full Wave rectification. and.v a. blocking con-- denser 46' is connected across the linehefcre the: filter comprising the shunt condenser 48. and the series, inductance 5.0, the blocking condenser act.- ing as the currentinterrupter A inthemanner illustrated inFig. 4. The. alternating current,volt-. age supplied by the source S is representedhy the. solid lines 52,52" andthe broken line 54-.-. The.- full. wave. rectified. voltage, applied. across thev blocking condenser 46' is representedjby the lines 52, 52 and the line 56'. The voltage attheblocking condenser is is represented by, the line 55. and. the current surges or pulses passing through, the circuit are represented by the, lines 66', 62 and 614. Th blocking condenser 45 is, after the circuit has been in operation, charged to a. value illustrated. by the beginning of the line 58, which value is for a considerable period of'time, reater than the instantaneous rectified voltage supplied. by the source S. Howeventhe voltage supplied by, thev source is increasing at the same tim that the. voltage of. the blocking condenser 45 is decreasing because of its discharge and at the. point 6'5 the rectified voltage 52, 55 or 52' exceeds, the blocking voltage of the condenser 45. It is at this point that the current starts to flow. The magnitude of the currentincreasesv until the magnitude of the rectified voltage reaches its maximum and". then the current starts to decrease along with the voltage. During the period of current how, the condenser 46' is recharged as indicated b rthecircuit, to so synchronize 6 upward slopeofrthe; portions 58. of; the linc158; Atthe; point 68, therectifiedvoltage 5.2, 56,011. 52. becomes less. thanrthe voltage condenser -46. andhence atthis. point the current falls off. The; rectified: voltage decreasesv at a. greater-rate. than the: condenser '46 discharges so itiisznocuntilithe'next point 6.5 is reached that any currentagain flows. Consequently, although the voltage from the source S is constantly alternatlng current flows inthe circuit only during discrete; surge periods.

It will therefore be apparent that if the phase. of the-,currentin the actuator-moving electrically energizedcoillfibe properly related to the other electrical and physical. constants of the system, once-again. the contact pairswill be opened only, during periods of no currentfiow and hence the current carrying capacity of. the regulator can be increased. In Fig. 3, the coil, 28. is connected 7 across the load after. the filter and hence the pule my invention is susceptible. While both full.

and half "wave rectifications have been here illustrated, it is not necessary that any rectification at all take place so long as the currentis, in some way; periodically interrupted. The specific phase shifting circuitsB here illustrated and the specific manners of connection are capable of an almost infinite number of variations all within the skill of those versed in; the art. Many ways of phase shifting are known and the precise manner-of-phase shifting is not of significance insofar as this invention is concerned. lvlechanical as well aselectrical phase shifting may be employed toachieve the desired results.

The fact" of significance is that the contact pairs, are connected'into a circuit the current in Which'ls intermittent and the actuator for the contact pairs is moved in timed or synchronous relation to the intermittent pulses or surges of current, the synchronization being such that the actuator is moved to open thecontacts only during those periods of time when no current is flowing in the circuit: While it is desirable that the closing of the contacts occur during the same periods-of no current-flow, this is not considered a necessary feature; since it has been noted that practically no damage occurs to the contacts when they close on large currents, whereas exceedingly great damage is done to the contacts, particularlyin small regulators, when they open while carrying large currents.

By the-invention herein described it is possible, by means of" a simple adjustment of a circuit element which forms a part of a phase shifting the operation of the regulator with the int of current carried thereby as to render even the smallest regulator capable of carrying exceedingly large currents over extended periods of time without malfunctioning. This characteristic'isof exceedingly great importance, particularly since the space and weight requirements of aircraft-carried and military equipment are very rigorous, making small size-regulators exceedingly useful.

58. of the blocking ermittent surges or pulses- Moreover, by means of this invention, exceedingly small finger type regulators are enabled to do the work of previously used much larger and more massive regulators the cost of which are from ten to one hundred times that of the small regulator.

It will be apparent that many detailed changes may be made in my invention within the spirit thereof as defined in the appended claims.

I claim:

1. A regulation system comprising a current source, a current interrupter, and a load connected in sequence, a plurality of regulatory circuit components in said circuit, a plurality of contacts electrically connected to said regulatory components and successively movable between open and closed positions so as to successively connect and disconnect said components in said circuit, an actuator operatively connected to said contacts and positionable over a range of movement so as to open and close said contacts, an electrically energized element connected in said circuit after said interrupter and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and phase shifting components in said circuit active on said element for controlling the phase or" the current in said element relative to the phase of current flowing through said contacts so that said contacts are opened only during the periods when said circuit is interrupted.

2. A regulation system comprising an alternating current source, a current interrupter, and a load connected in sequence, a plurality of regu latory circuit components in said circuit, a plurality of contacts electrically connected to said regulatory components and successively movable between open and closed positions so as to successively connect and disconnect said components in said circuit, an actuator operatively connected to said contacts and positionable over a range of movement so as to open and close said contacts, an electrically energized element connected across said load after said interrupter and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and phase shifting components in said circuit active on said element for controlling the phase of current in said element relative to the phase of current flowing through said contacts so that said contacts are opened only durin the periods when said circuit is interrupted.

3. A regulation system comprising an alternating current source, a rectification circuit capable of producing pulsating direct current, and a load connected in sequence, a plurality of regulatory circuit components in said circuit, a plurality of contacts electrically connected to said regulatory components and successively movable between open and closed positions so as to successively connect and disconnect said components in said circuit, an actuator operatively connected to said contacts and positionable over a range of movement so as to open and close said contacts, an electrically energized element connected across said load after said rectification circuit and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and phase shifting components in said. circuit active on said element for controlling the phase of current in sail element relative to the phase of current flowing through said contacts so that said contacts are opened only during the periods between the pulses of direct current.

7 4." A re'g ulation system comprising an alternat ing current source, a half wave rectifier and a load connected in sequence, a plurality of regulatory circuit components in said circuit before said rectifier, a plurality of contacts electrically connected to said regulatory components and successively movable between open and closed positions so as to successively connect and disconnect said components in said circuit, an actuator operatively connected to said contacts and positionable over a range of movement so as to open and close said contacts, an electrically energized element connected across said load after said rectifier and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and phase shifting components in said circuit active on said element for controlling the phase of the current in said element relative to the phase of current flowing through said contacts so that said contacts are opened only during the periods between the surges of direct current.

5. A regulation system comp-rising an alternating current source, a full wave rectifier and a load connected in sequence, a condenser connected across said load and effective to periodically interrupt the current supplied by said source, a plurality of regulatory circuit components in said circuit before said rectifier, a plurality of contacts electrically connected to said regulatory components and successively movable between open and closed positions so as to successively connect and disconnect said compoents in said circuit, an actuator operatively connected to said. contacts and positionable over a range or movement so as to open and close said contacts, an electrically energized element connected across said load after said rectifier and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and phase shifting components in said circuit active on said element for controlling the phase of the current in said element relative to the phase of current flowing through said contacts so that said contacts are opened only during the periods when the current from said source is interrupted.

6. A regulation system comprising an alternating current source, a half wave rectifier and a load connected in sequence, a plurality of resistors connected in series in the alternating current portion of the circuit, a plurality of contacts electrically connected to said resistors, successively movable between open and closed positions, and active to successively short-circuit said resistors and thus remove them from said circuit, an actuator operatively connected to said contacts and positionable over a range or" movement so as to open and close said contacts, a coil connected across said load in the rectified por-v tion of the circuit and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and a capacitance connected in shunt across said coil, the value of said capacitance being so chosen as to control the phase of current in said coil relative to the phase of current flowing through said contacts so that said actuator opens said contacts only during the periods between the surges of direct current.

7. A regulation system comprising an alternating current source, a full wave rectifier and a load connected in sequence, a blocking condenser connected across said load and effective to periodically interrupt the current supplied by said :source, a plurality of resistors connected inseries in the alternating-current portion-'of'the circuit, a plurality of contacts electrically connected to said resistors, successively movablerbetween -open and closed positions, and "active to successively short-circuit said resistors and thus remove them from said circuit, an actuator-operatively connected to said -.contacts and positionable over a range of movement so as to open and close said contacta-a-coil connected :across said =load "and active on said actuator "to control its position and thus determine which of said contacts are opened or closed, and a phase shifting circuit connected between one end of said coil and a portion of the direct current part of said circuit having pulsating current flowing therethrough, the value of the circuit components of said phase shifting circuit being so chosen as to control the phase of the current in said coil relative to the phase of current flowing through said contacts so that said actuator opens said contacts only during the periods when the current from said source is interrupted.

8. A regulation system comprising a current source, a current interrupter, and a load connected in sequence, aplurality of regulatory circuit components in said circuit before said interrupter, a plurality of contacts electrically connected to said regulatory components and successively movable between open and closed positions so as to successively connect and disconnect said components in said circuit, an actuator operatively connected to said contacts and positionable over a range of movement so as to open and close said contacts, an electrically energized element connected in said circuit after said interrupter and active on said actuator to control its position and thus determine which of said contacts are opened or closed, and means for varying the inertia of the actuator-contacts combination so that said contacts are opened only during the periods when said circuit is interrupted.

9. The regulation system comprising a circuit, means in said circuit for periodically interrupting the current therein, regulating means in said circuit comprising regulatory circuit components and circuit-breaking elements operatively connected thereto so as to connect or disconnect said components in said circuit, operating means operatively connected to said circuit-breaking elements to open or close the latter, and means to actuate said operating means in synchronism with the periodical interruption of current in said circuit so as to open said elements only when said circuit is interrupted.

10. The regulation system comprising a circuit, means for supplying said circuit with intermittent current, regulating means in said circuit comprising regulatory circuit components and circuit-breaking elements operatively connected thereto so as to connect or disconnect said components in said circuit, operating means operatively connected to said circuit-breaking elements to open or close the latter, and means to actuate said operating means in synchronism with the current in said circuit so as to open said elements only when said current is flowing.

11. The regulation system comprising a circuit, means for supplying said circuit with rectified pulsating direct current, regulating means in said circuit comprising regulatory circuit components and circuit-breaking elements operatively connected thereto so as to connect or disconnect said components in said circuit, operating means 10 operatively connected to said circuit-breaking elements ate-open oraclose the latter, and means to actuate said operating means in synchronism .withithe current in said circuit. soas to open said .elements only during -thejperiods between said direct current pulses.

fI2. A;r egulation system comprising a circuit, .meansffor supplying said circuit with. half-wave .rectifiedrdirect current, regulating means in said circuit comprising regulatory circuit components .and circuit-breaking elements operatively connecte'd'thereto so asto connector disconnect said components in said circuit, operating means operatively connected to said circuit-breaking elements to open or close the latter, and means to actuate said operating means in synchronism with the current in said circuit so as to open said elements only during the periods between said direct current pulses.

13. A regulation system comprising a circuit, means for supplying said circuit with pulsating full wave rectified current, regulating means in said circuit comprising regulatory circuit components and circuit-breaking elements operatively connected thereto so as to connect or disconnect said components in said circuit, operating means operatively connected to said circuitbreaking elements to open or close the latter, and means to actuate said operating means in synchronism with the current in said circuit so as to open said elements only during the periods between said direct current pulses.

14. In the regulation system of claim 9, electrical connections between said circuit and said actuating means so as to energize the latter from the former, said connections including means to control the phase of the energizing current supplied to said actuating means relative to the phase of the interrupted current in said circuit.

15. In the regulation system of claim 10, electrical connections between said circuit and said actuating means so as to energize the latter from the former, said connections including means to control the phase of the energizing current supplied to said actuating means relative to the phase of the intermediate current in said circuit.

16. In the regulation system of claim 11, electrical connections between said circuit and said actuating means so as to energize the latter from the former, said connections including means to control the phase of the energizing current supplied to said actuating means relative to the phase of the pulsating current in said circuit.

1'7. In the regulation system of claim 12, electrical connections between said circuit and said actuating means so as to energize the latter from the former, said connections including means to control the phase of the energizing current supplied to said actuating means relative to the phase of the pulsating current in said circuit.

18. In the regulation system of claim 13, electrical connections between said circuit and said actuating means so as to energize the latter from the former, said connections including means to control the phase of the energizing current supplied to said actuating means relative to the phase of the pulsating current in said circuit.

19. In the regulation system of claim 9, electrical connections between said circuit and said actuating means so as to energize the latter from the former, and means for controlling the inertia of the mechanical moving parts of the system including said circuit-breaking elements.

ARTHUR M. COHEN.

(References on following page) 11 References Cited in the file of this patent UNITED STATES PATENTS Number Name Date McDonell Apr. 8, 1902 5 Wappler Sept. 12. 1911 Amsden July 10, 1928 Hendry July 1, 1930 Kearsley Aug. 25, 1931 Lee Oct. 13, 1931 10 Madden Oct. 29, 1935 Koppelmann Jan. 30, 1940 Number Number Name Date Koppelmann et a1. Apr. 2, 1940 Koppelmann Mar. 17, 1942 Zuhlke Feb. 2, 1943 Zelleweger July 11, 1944 Scheg Jan. 9, 1945 Kovalsky Jan. 13, 1948 FOREIGN PATENTS Country Date Great Britain Oct. 29, 1928 

